Industrial and power generation gas turbines have control systems that monitor and control their operation. These control systems may be designed to meet the power and efficiency objectives while governing operational aspects of the gas turbine.
Current control systems may execute scheduling algorithms that adjust the fuel flow, inlet guide vanes (IGV), and other control inputs to provide safe and efficient operation of the gas turbine. Gas turbine control systems typically receive as inputs operating parameters and settings that, in conjunction with scheduling algorithms, determine turbine control settings to achieve the desired operation. Measured operating parameters may include, but are not limited to, compressor inlet pressure and temperature, compressor exit pressure and temperature, turbine exhaust temperature, and generator power output. Desired operating settings may include, but are not limited to, generator power output and exhaust energy. The schedules (e.g., exhaust temperature vs. compressor pressure ratio, fuel splits vs. combustion reference temperature, inlet bleed heat vs. ICV, compressor operating limit line vs. corrected speed and inlet guide vane, etc.) are typically defined to protect the turbine against known operational boundaries (e.g., emissions, dynamics, lean-blow-out, compressor surge, compressor icing, compressor clearances, aero-mechanical, etc.) based on off-line field tests or laboratory data. The output of the schedules then determines the appropriate adjustment of the control system inputs. Typical control inputs (also referred to as “effectors”) managed by a control system may include, but are not limited to, fuel flow, combustor fuel distribution (which may be referred to as “fuel splits”), compressor inlet guide vane, and inlet bleed heat flow.
However, forcing strict turbine compliance with schedule-based control systems can cause performance to be sacrificed at many operating conditions in an effort to protect against worst-case operational boundaries. Additionally, rigid schedule-based control systems may not provide a relatively simple means for identifying and incorporating component deterioration while controlling the operation of the gas turbine. For example, as the machine is operated the components may foul or degrade, which may in turn alter the characteristics of one or more of the operational boundaries. Without identifying the deterioration as it occurs, the system will either have to be re-tuned periodically, have boundaries set artificially low (or high as some boundaries might require) to preemptively accommodate component deterioration, or risk violating operational boundaries that may lead to excessive fatigue or failure. Similarly, schedule-based control systems may also not be able to effectively accommodate changing conditions (e.g., gas quality, ambient conditions, or other un-modeled disturbances) to either tune for the most efficient operation or to avoid violation of component operational limits. Another disadvantage to schedule-based control systems is the resultant coupling that may occur between different turbine control effectors which creates inflexible tuning and may prohibit operating turbines at their optimized levels. For example, fuel splits depend on the firing temperature, which is in turn proportional to the exhaust temperature, which is often scheduled with compressor pressure ratio. In this scenario, a change to the exhaust temperature schedule may necessarily require changing the fuel split schedule.
Thus, there exists a need for methods and systems for model-based control systems of gas turbines.